Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine

PubMedID: 24006042

Often researchers use kinematics and kinetics to evaluate the effect of limb pathology. The net forces and moments that cause motion depend on kinematics, body segment parameters and the external loads applied. This study aimed to evaluate the discrepancies caused by different methods and assumptions of kinetic analysis. Dynamic analysis was performed on 12 subjects with no known pathology while performing 12 activities of daily living. The recursive Newton-Euler method, along with two robotic models containing 7 and 14 degrees of freedom representing the upper limb, was used to calculate the net forces and moments across the shoulder. The data were calculated using different body segment parameter values from the literature and, in order to concentrate on the effects of kinematics only, these results were presented as both a percentage of the body weight and a novel technique using constant body segment parameter. The greatest net forces and moments on the glenohumeral joint were observed for lifting a 2-kg shopping bag task (forces: 60 ± 8 N and moments: 18 ± 2 N m) and the lowest was observed for drinking (forces: 40 ± 8 N and moments: 6 ± 1 N m). Overall, the results from different techniques (recursive Newton-Euler vs robotic 14 degrees of freedom) were similar, while the 7-DoF model showed less agreement. The use of different body segment parameter values resulted in a maximum increase of 25% in the glenohumeral moment. Following normalisation of the body segment parameter, dynamic parameters were found to have less variation. In order to focus on the effect of variation in movement in dynamic study, it is therefore necessary to normalise the body segment parameter.